Experimental and analytical study on properties affecting the behaviour of FRP-confined concrete

In this study the results of a large test program are presented with the objective of examining the effect of various experimental parameters on the confinement effectiveness of FRP jackets on both circular and rectangular concrete columns with solid or hollow core. The experimental parameters include: different concrete strength, type of fibres, number ofwrap layers, geometry of the column, corners radius, full/hollow core and cross-sectional aspect ratio (only for prismatic elements). FRP-confined and unconfined specimens have been loaded in uniaxial compression until failure. Totally 128 specimens were prepared and tested, 89 of them were strengthened with Carbon FRP (CFRP) and Glass FRP (GFRP), the remaining 39 were tested as plain concrete reference. Compressive stress, axial and hoop strains have been measured to evaluate the stress–strain relationships, ultimate strength, stiffness, and ductility of the specimens. Results confirmed that external confinement produced by FRP can significantly enhance compressive strength, ductility and energy absorption capacity if compared to those of plain concrete. The effects of test parameters are evidenced and compared in order to show the sensitiveness of the mechanical problem for each of them. Important design information are furnished to researchers and practitioners also by comparing the results of the experimental campaign with the prediction of different analytical models, based on well-known and widely accepted mechanical assumptions. Design equation recommended by CNR (Italian National Research Council) were also applied by assuming unitary values for safety factors, in order to see the reliability of the mechanical model proposed by CN

FRP-Confinement of Hollow-Core Concrete Cylinders and Prisms

The use of hollow-core reinforced concrete (RC) sections for bridge piers has become a popular engineering practice to obtain a reduction of the self-weight (especially in seismic zones) and a better structural efficiency in terms of the strength/mass and stiffness/mass ratios. In contrast to this popularity in practice, scientific studies on the mechanical behavior of such structural elements are limited. The use of Fiber Reinforced Polymer (FRP) materials for external confinement of hollow core columns and piers is an almost unknown field at the moment. The research work presented herein aims at evaluating the influence of various experimental parameters on the effectiveness of FRP jackets applied to hollow concrete columns. Hollow-core concrete prisms and cylinders were tested under uniaxial compression to study the stress-strain relationship before and after FRP jacketing. A range of experimental parameters were investigated: different concrete strength, type of fibers, number of wrap layers, column shape and dimensions, and for square and rectangular sections, the corner radius and the cross-sectional aspect ratio. Axial strain was measured by LVDTs, while strains in the fibers were recorded by electrical strain gauges. Circular columns wrapped with FRP showed a significant increase in terms of both strength and ultimate displacements. Results obtained by laboratory tests were close to those recorded for FRP-confined concrete, which means that the increase in ultimate load was found to be comparable to that found in full circular sections. Rectangular columns showed a lower increase in ultimate capacity, compared to circular sections, even if the results related to ultimate axial displacement encourage adopting this technique for seismic retrofit to fulfill higher ductility requirements in both prismatic and cylindrical columns

FRP-Confinement of Concrete Cylinders and Prisms

The use of fibre reinforced polymer (FRP) composites has been successfully promoted for external confinement of reinforced concrete (RC) columns and pillars all over the world. Increase in compressive capacity and energy absorption before collapse have been largely experienced in laboratory environment during the last decade, especially by testing concrete cylinders wrapped with FRP jackets. In this study the results of a large test program are presented with the objective of examining the effect of various experimental parameters on the confinement effectiveness of FRP jackets on both circular and rectangular concrete columns. The experimental parameters include: different concrete strength, type of fibres, number of wrap layers, geometry of column, corners radius and cross-sectional aspect ratio for rectangular columns. FRP-confined and unconfined specimens have been loaded in uniaxial compression. Compressive stress, axial and hoop strains have been measured to evaluate the stress-strain relationships, ultimate strength, stiffness, and ductility of the specimens. Results confirmed that external confinement produced by FRP can significantly enhance strength, ductility and energy absorption capacity if compared to those of plain concrete. The effects of test parameters are evidenced and compared; important design information is furnished to researchers and practitioners

Stress strain relationship of FRP-confined concrete for hollow columns

Past studies demonstrated the structural efficiency of FRP-confinement for reinforced concrete (RC) columns to increase their strength and ductility in axial compression [1-4]. Numerical and analytical models were developed to predict the stress-strain behavior of FRP confined concrete [5-8] and recommendations were provided to practitioners for design of FRP-retrofitted RC columns. Scientific studies related to FRP-confinement of hollow-core RC columns are very limited at the moment; a few data reporting properties of RC hollow-core columns under seismic forces are available [9-11]. This clashes with the thousands of applications all over the world in which bridge piers are designed as hollow-core columns to maximize the structural efficiency in terms of strength/mass and stiffness/mass ratios. In this work both solid and hollow-core concrete prisms and cylinders were tested under uniaxial compression to study the influence of various experimental parameters on the effectiveness of FRP jackets applied to concrete columns subjected to uniaxial compression loading. The investigated parameters were the concrete strength, the fibers type, the number of wrap layers, the column shape and dimensions and, for prismatic sections, the corner radius and the cross-sectional aspect ratio. On the basis of the experimental results obtained, a nonlinear finite element model was developed, obtaining a good correlation between the experimental and the numerical data in terms of stress-strain curves and ultimate load

Appraisal of salt tolerance under greenhouse conditions of a cucurbitaceae genetic repository of potential rootstocks and scions

Soil salinization due to climate change and intensive use of water and soil is increasing exponentially. Cucurbitaceae species are cultivated worldwide and the identification of salinity tolerant genotypes to be used as rootstock or scion for securing yield stability in salt affected agricultural areas is a research priority. In the present greenhouse study, we assessed the response to salinity (0 mM a non-salt control and 150 mM NaCl dissolved in the nutrient solution) in the seedlings of 30 genotypes of cucurbits grown in a floating hydroponic system. The species tested included 16 genotypes of Cucumis melo L. (CM1-16), 6 Citrullus vulgaris Schrad. (CV1-6), 2 interspecific hybrids of Cucurbita maxima Duch. × Cucurbita moschata Duch. (CMM-R1 and 2), 4 bottle gourd (Lagenaria siceraria (Molina) Standl. (LS1-4)), 1 Cucurbita moschata Duch. (CMO51-17), and 1 luffa (Luffa cylindrica Mill. (LC1)) species. Results highlighted different morphological and physiological traits between the species and genotypes and a different response to salt stress. We identified C. maxima × C.moscata interspecific hybrid CMM-R2, melon genotypes CM6, CM7, CM10, and CM16 together with watermelon genotypes CV2 and CV6 and bottle gourd LS4 as salt tolerant genotypes and possible candidates as salt resistant rootstock to be introduced in grafting programs

Reviewing chemical and biological risks in urban agriculture : A comprehensive framework for a food safety assessment of city region food systems

Attention to urban agriculture (UA) has recently grown among practitioners, scientists, and the public, resulting in several initiatives worldwide. Despite the positive perception of modern UA and locally grown, fresh produce, the potential food safety risks connected to these practices may be underestimated, leading to regulatory gaps. Thus, there is a need for assessment tools to evaluate the food safety risks connected to specific UA initiatives, to assist practitioners in self-evaluation and control, and to provide policy makers and scholars a means to pursue and assess food safety in city regions, avoiding either a lack or an excess of regulation that could ultimately hinder the sector. To address this aim, this paper reviews the most recent and relevant literature on UA food safety assessments. Food safety indicators were identified first. Then, a food safety assessment framework for UA initiatives was developed. The framework uses business surveys and food analyses (if available) as a data source for calculating a food safety index for single UA businesses and the whole UA landscape of a given city region. The proposed framework was designed to allow its integration into the CRFS (City Region Food System) toolkit developed by FAO (Food and Agriculture Organization of the United Nations), RUAF foundation (Resource Centres on Urban Agriculture and Food Security) and Wilfrid Laurier University.</p

Reviewing chemical and biological risks in urban agriculture: A comprehensive framework for a food safety assessment of city region food systems

Attention to urban agriculture (UA) has recently grown among practitioners, scientists, and the public, resulting in several initiatives worldwide. Despite the positive perception of modern UA and locally grown, fresh produce, the potential food safety risks connected to these practices may be underestimated, leading to regulatory gaps. Thus, there is a need for assessment tools to evaluate the food safety risks connected to specific UA initiatives, to assist practitioners in self-evaluation and control, and to provide policy makers and scholars a means to pursue and assess food safety in city regions, avoiding either a lack or an excess of regulation that could ultimately hinder the sector. To address this aim, this paper reviews the most recent and relevant literature on UA food safety assessments. Food safety indicators were identified first. Then, a food safety assessment framework for UA initiatives was developed. The framework uses business surveys and food analyses (if available) as a data source for calculating a food safety index for single UA businesses and the whole UA landscape of a given city region. The proposed framework was designed to allow its integration into the CRFS (City Region Food System) toolkit developed by FAO (Food and Agriculture Organization of the United Nations), RUAF foundation (Resource Centres on Urban Agriculture and Food Security) and Wilfrid Laurier University